Sleep apneas are recognizable interruptions of breathing and are classified as central, obstructive, or mixed. Central apneas are characterized by a cessation of airflow at the nose and mouth with no apparent respiratory effort and are the consequence of a cessation in the phasic central neural drive to breathe In contrast, obstructive apneas are seen when there is a cessation of airflow at the nose and mouth but continued respiratory effort; they are particularly likely to occur during rapid eye movement sleep. The respiratory efforts during an obstructive apnea are rendered ineffective by the loss of upper airway patency because of collapse. It is also possible to have partial airway obstruction when the airway patency is reduced This condition is characterized by increased respiratory effort but diminished airflow in response to increased upper airway resistance. Mixed apneas are described when elements of central and obstructive apneas are seen in association. The length of apnea considered abnormal varies with age. Premature infants, for example, may exhibit central apneas of up to 20 seconds' duration before they are considered abnormal, whereas older infants and children may exhibit shorter periods of clinically significant obstructive apnea Its association with significant hypoxia, hypercapnia, or bradycardia may be a measure of the significance of an apnea.
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